I just did this yesterday too! Along with two of my co-workers with GT's. My car has no cats at all, I tried stage 2 and it was pretty fun but waaayyy too loud, I went back to stage 1 and it great!!!!
You can say what you want, but my car spools alot faster now, and the car ghas more pull. I think since I have no cats at all, the big bottle neck was the mufflers, with the washers in there it flows right out. I fyou dont believe me, and are on the south shore swing by and we'll go for a ride!